In a fiberoptic network, optical signals are encoded with digital streams of information and transmitted through a series of spans of optical fiber. At a receiver end, the optical signals are detected and decoded by a receiver. In Fiber to the Home (FTTH) applications, modulated optical carrier signals are used to relay broadband coaxial cable signals to and from end users. Similarly, in Fiber to the Antenna (FTTA) applications, modulated optical carrier signals are used to relay broadband radio frequency (RF) signals to and from antennas. In FIT A applications, a single optical fiber is used for bidirectional transmission, with a 1550 nm wavelength band being typically used for downstream transmission from a central station to an RF antenna, and a 1310 nm wavelength band used for an upstream transmission, that is, from the RF antenna back to the central station.
As passive fiberoptic links find an increasing use, so increase occurrences of fiber breakage, faulty fiber connections, open fibers, etc. A fiber breakage, or a mere deterioration of a fiber transmission, may occur during normal operation of a passive fiberoptic link. Thus, a need exists for monitoring fiber network integrity and performance level.
One drawback of prior art monitoring systems is that a precise location of the fiber breakage point in a fiberoptic network is unknown. Since fiberoptic network may span for leas and even hundreds of kilometers in some cases, it is desirable that a monitoring system have a fiber break locating functionality.
One known method of determining a distance to a fiber breakage is Optical Time-Domain Reflectometry (OTDR). In OTDR, a powerful laser pulse is launched at a proximal end of a fiberoptic link, and a time dependence of the reflected light power is monitored. Since speed of light in the fiberoptic link being tested is known, the distance to a fiber breakage point may be determined by measuring a time delay between the launched pulse and a pulse reflected from the fiber breakage point. OTDR, however, may disturb normal operation of a fiberoptic link, because the powerful laser pulse may interfere with optical data transmission. Furthermore. OTDR output data are rather complex, and require trained personnel to interpret.